1. Field of the Invention
The present invention broadly relates to a method and apparatus for manufacturing almost any object which includes at least one part formed of a folded sheet material. More particularly, the present invention relates to a continuous method and apparatus for manufacturing said part out of said sheet material. In one embodiment, the invention relates to a continuous method and apparatus for making stringers and cross stringers and assembling them into cardboard pallets.
2. Description of the Prior Art
The present invention relates to improvements to the method and apparatus disclosed in earlier U.S. Pat. No. 4,792,325 issued Dec. 20, 1988, and entitled "METHOD AND APPARATUS FOR MANUFACTURING CARDBOARD PALLETS", which is the most pertinent prior art of which we are aware.
Such method and apparatus proved entirely satisfactory as long as no design changes had to be made in the pallet produced thereby. However, as recyclable cardboard pallets became more and more popular, and were used for heavier and heavier loads, for certain applications the pallet made by said method and apparatus proved unsatisfactory. The stringers and cross stringers of said pallet, which had to be symmetrical because of the limitations of the method and apparatus, could not be folded tight enough to make stronger members. Also, the stringers were not glued to the cross stringers, and under certain conditions, vibrations had an adverse effect.
Also, the very nature of the recycling process resulted in pressure from the users of recyclable pallets to make changes in the method and apparatus practiced by said U.S. Pat. No. 4,792,325. Because the recycling process essentially involves a shredding as its first step, in any objects made with hot glue, the heat turns the glue soft, and the glue then clogs the shredder. Because of this there has been a growing demand that paper products, and especially pallets, be made with cold glue. The advance of pallet making technology has allowed for the spray application of cold glue which was only being contemplated when the apparatus of said U.S. Pat. No. 4,792,325 was being developed.
A pallet is also more easily recyclable if the glue throughout the product is the same. Because the glue used in making the corrugated cardboard is a cold glue, it is additionally desirable that the disposable pallet be assembled with cold glue. All the glue in the produce will then be water based cold glue which will simply dissolve during the shredding and recycling process. Even if a non-water based cold glue is used to make waterproof cardboard constructions, the fact that the glue will not soften in the shredder aids in the recycling process. All of these factors made the design of a stronger, cold glued, disposable cardboard pallet mandatory.
When such a pallet was designed, several things were discovered. First, for increased strength it would be desirable if the cross stringers were of a different shape than the stringers. Secondly, it was found in the preferred embodiment of the pallet that the shape of the cross-stringer, was nonsymmetrical, and the blank used to manufacture it was nonsymmetrical. Thirdly, it was found that such a nonsymmetrical blank could not be folded symmetrically from both sides at the same time, as required by said U.S. Pat. No. 4,792,325, making a redesign of the apparatus necessary. Lastly, it was found out that if compression could be maintained on the cardboard during the folding operation, a stronger member would be produced. The old apparatus simply was incapable of doing this, although several attempts were made.
For ease of understanding, the term "asymmetrical" will be used in the present application to designate any type of folding where the folding operation does not take place from the outside simultaneously (i.e., the blank of sheet material is being folded from only one side at a time), while the term "nonsymmetrical" will be used to refer to the cross section of a stringer or a cross stringer. It should also be understood that the term "asymmetrical" still applies to the folding operation, even if the pallet is repeatedly folded from one side, and whether it is ever folded from the other side.
When asymmetrical folding was tried using curvilinear rod means similar to those disclosed in U.S. Pat. No. 4,792,325, problems immediately arose. It was found that since folding pressure was being applied from one side at a time, in contrast to being applied evenly from both sides as in said prior patent, hold-down means similar to those used in the prior apparatus were completely inadequate, and the blanks would tend to twist and jam the machine.
Furthermore, when stronger hold-down pressures were applied, it was found that the machine would jam because the combination of the increased hold-down pressures, and the friction applied by the continuous rod means, were so great that the machine simply did not have power enough to propel the blanks longitudinally therethrough. Increasing the power of the machine also did not overcome the problems presented by trying to make asymmetrical folds. Also, the prior apparatus could not satisfactorily be modified to keep a member in compression while folding the same.
After much experimentation, it was found that the continuous rod means in the previous machine had to be completely discarded and replaced with a multifunctional folding means which not only folded the cardboard blank as it progressed longitudinally through the machine, but aided the drive belt used in propelling the blank through the machine, and compressed the member while folding, if desired. When this was done, it was found that a universal method and apparatus was provided which could symmetrically or asymmetrically fold a symmetrical or nonsymmetrical cardboard blank to produce symmetrical or nonsymmetrical cardboard parts. The parts can be assembled to form objects such as parts containers and the like. The parts can be produced under compression, if desired.